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Transcript abundance of phytoene synthase 1 and phytoene synthase 2 is associated with natural variation of storage root carotenoid pigmentation in carrot

Bowman, Megan J., Willis, David K., Simon, Philipp W.
Journal of the American Society for Horticultural Science 2014 v.139 no.1 pp. 63-68
Daucus carota, biosynthesis, carotenoids, carrots, color, gene expression, genes, genotype, leaves, messenger RNA, mutation, nutrients, phytoene synthase, pigmentation, plant tissues, polymerase chain reaction, roots
Carotenoids are isoprenoid compounds synthesized in plants which serve as photoprotectants and provide plant tissues with red, orange and yellow pigmentation. These compounds are important in human health, as they serve as both vitamin A precursors as well as having antioxidant properties. Carrot provides an important source of carotenoids in the human diet, providing up to 30% of pro-vitamin A in the United States. While essential to human health, very little is currently understood about the accumulation of carotenoids in carrot. To better understand the molecular mechanism for carotenoid accumulation in carrot we used real time quantitative PCR to evaluate the expression of nine genes in the carotenoid biosynthetic pathway in storage root tissue. No significant difference was found among white, yellow, orange, and dark orange carrot roots in seven of the nine genes evaluated, but relative to yellow and white carrots, increased phytoene synthase 1 and phytoene synthase 2 expression was observed in orange and dark orange carrot roots. Increased phytoene synthase 1 and 2 expression was not observed in the leaf tissue of these genotypes, indicating a different mechanism for carotenoid accumulation in the leaf tissue of carrot. This study is the first to demonstrate that naturally-occurring mutations that dramatically increase carotenoid accumulation in orange carrot are associated with increased phytoene synthase 1 and 2 expression and it provides insights into the mechanism underlying the biosynthesis of these important nutrients.